1. Field of the Invention
The present invention relates to a lighting device, especially to a lighting device having multiple LED light bars.
2. Description of the Related Art
In recent years, lighting devices generally use incandescent bulbs or high-power LEDs as light sources. Conventional incandescent bulbs are gradually being replaced in many applications by LED light source because incandescent bulbs have disadvantages of high power consumption, low luminous efficiency, and being renewed frequently due to a short life span. Compared with the conventional incandescent bulbs, LEDs offer advantages of high efficiency, low power consumption and a relatively long lifetime.
With reference to FIG. 11, a conventional LED lighting device applied as a streetlight may have a heat-dissipating base (42), an aluminum circuit board (41), multiple high-power LED modules (40) and a cover (43). The heat-dissipating base (42) has multiple fins. The aluminum circuit board (41) is attached to a plane surface of the heat-dissipating base (42). The high-power LED modules (40) are electrically mounted on the aluminum circuit board (41) by soldering. The cover (43) is mounted on the heat-dissipating base (42) and covers the high-power LED modules (40). When applying to be a streetlight, the conventional LED lighting device is adapted to be mounted on a top end of a streetlight post to provide illumination on a street at night. When the conventional LED lighting device is turned on, the high-power LED modules (40) generate heat and the heat will be conducted to the heat-dissipating base (42) for dissipation.
Although the foregoing conventional LED lighting device can provide illumination to streets, the LED lighting device still has some shortcomings:
1. Not easy to repair: since the high-power LED modules are soldered on the aluminum circuit board, when one of the high-power LED modules fails, a normal person cannot only change the broken one with simple tool such as a solder, but need a professional technician to disconnect the aluminum circuit board, and then sends the whole aluminum circuit board with the high-power LED modules or the full set of streetlight back to the factory for fixing. Therefore, the cost of repair is very high.
2. Low heat-dissipation efficiency: A large amount of high-power LED modules is required in a conventional LED lighting device, such as a streetlight, to provide sufficient lights. However, large amounts of heat are produced when activating high-power LED modules. When all the heats from each module are conducted to the heat-dissipating base, it will double the heat accumulating and cause heavy loading for the heat-dissipating base.
Due to consideration of installing the LED lighting device in a high position, the aluminum circuit board and the heat-dissipating base are normally limited in size and weight. With such limitation, the LED lighting device is hard to effectively dissipating heat when the heat-dissipation base was not well designed. Therefore, operating the high-power LED modules in high temperature without effective heat dissipation may eventually lead to device failure and may also result in overheating of other electronic components on the circuit board and shortening of their life spans.
3. Limited illumination area: The conventional LED lighting device provides a substantial round-shaped illumination area. The luminous intensity of the round-shaped illumination area decreases as leaving the center of the illumination area. To meet requirements of a street illumination when being applied as a streetlight, an oval-shaped illumination area is required. Therefore, the aluminum circuit board and the heat-dissipating base all have to be changed in structure. Designing the structure to meet different kinds of illumination-area may require a lot of different molds and high cost.
To overcome the shortcomings, the present invention provides a lighting device to mitigate or obviate the aforementioned problems.